1. Field of the Invention
The present invention relates to laser labels and their use for anti-counterfeit marking.
2. Description of Related Art
Technical labels are employed in numerous sectors for high-grade applications--for instance, as model identification plates for vehicles, machines, electrical and electronic appliances, as control labels for process sequences, and as badges of guarantee and testing. In numerous instances these applications automatically entail the need for a greater or lesser degree of security against counterfeiting. This counterfeiting security applies primarily for the period of application and for the entire duration of use on the part to be labelled: removal or manipulation should, if possible at all, entail destruction or visible, irreversible alteration. In particularly sensitive fields of application there must be a security stage for the production of the labels as well: if the acquisition and marking of such labels were too easy, and if imitations were produced, unauthorized persons would be given the possibility of improperly trafficking in the articles concerned.
For the rational and variable production of high-grade labels, especially in technoindustrial applications, the laser marking of suitable base material is becoming increasingly more established. DE U 81 30 861.2 describes a multilayer label in which a top layer differing in colour is removed by the laser beam and, as a result, the contrast in colour with the adjacent layer permits inscriptions of high quality and legibility. Such an inscription constitutes a type of gravure, but removes the possibilities for manipulation associated with traditional printing with inks. DE U 81 30 861.2 entails the label film being rendered so brittle, by means of the raw materials employed and the production process, that it is impossible to remove the bonded labels from their substrate without destroying them.
An additional security stage is described in the single-layer laser label of DE U 94 21 868: here, in addition to the advantageous properties of DE U 81 30 861.2, the inscription is brought about not by gravure in the top layer but by a change in colour in the polymer layer itself, thereby very substantially preventing subsequent manipulation of the inscriptions.
Consequently, the only potential missing link in the security chain is that such single-layer and multilayer labels are freely available for laser inscription--for goods of appropriately high value, therefore, the acquisition of the labels and their inscription, even with expensive laser equipment, might be regarded as possible and rewarding.
In order to close the chain it was the aim of the development to configure the material from the which the labels are made in such a way, for their subsequent inscription, that such material can be identified at any time, with little effort and no destruction, as authentic, original material. For the laser labels which have already been specified, subsequent identification, although possible in principle, is nevertheless bound up with unacceptable analytical effort and is destructive.
Diverse techniques of ensuring security against counterfeiting are known for particularly security-relevant products, such as bank notes, cheques, cheque cards and personnel ID cards, inter alia. In addition to water marks, printing with intricate patterns, and application of holograms, "invisible" markings are also occasionally employed.
JP 08/1328474 describes a textile clothing label which is printed on its top face with a transparent, fluorescent ink, it being intended for the woven design and the printed image to be approximately identical in overlap. A similar surface printing with UV-active, photochromic inks is described in WO 88/01288; in order to protect the chemicals, however, this ink layer requires an additional layer for protection against oxygen and water.
In FR 2734655 a security marking on cheques is achieved in that, in part, the printing under a layer which is permeable only to IR is invisible in the visible wavelength range but can be read/identified mechanically with special IR light.
EP 727316 achieves hidden security against counterfeiting by providing, in an extra layer, especially on paper, two reactive components which give a colour reaction under pressure--this reaction, however, is irreversible.
The use of electroconductive and/or magnetic inks for surface printing is described in JP 08/1054825 and CN 1088239. For label applications on complex metal parts, such as vehicle and machine components, for example, the fitness of such systems for use is extremely limited.
The ink ribbons with fluorescent particles described in JP 07/164 760, which can be excited by IR, are transferred by means of heat, with thermal transfer printers. Although it is true that the prints constitute a hidden sign of originality, the printing is applied superficially and can be altered or removed with solvents, with heat or else mechanically.
DE 4231800 describes labels which for security against counterfeiting leave irremovable traces on the bonding substrates by means of supplimation inks or corrosive substances--in order to identify the traces, however, it is first necessary to remove the label, which is in many cases undesirable if not impossible.
For high security papers such as passports, shares, bank notes, etc., EP 453131 describes the incorporation into an interlayer between two permanently bonded plies of paper, along with the laminating adhesive, of fluorescent, especially UV-fluorescent, indicators which are detectable only on transmission of light of appropriate wavelength through the laminate but not by reflection under incident light. This system is unsuited to applications where transmission of light through the bonded label is impossible, and for the totally opaque laser labels.
All of these methods are applied superficially or are effective superficially and are therefore useful only to an extremely restricted extent if at all for the known laser labels, since in this case the surface of high optical quality and extreme resistance used, for example, for model identification plate applications would be altered and impaired. Such a modification would be particularly disruptive to the two-layer labels with high-gloss black top layer and white base layer that may be regarded as the technical standard for model identification plates. In addition, the means of security against counterfeiting that are known from the prior art and are applied superficially and subsequently carry with them the potential for manipulation to be carried out mechanically or using heat, chemicals, etc.